Ensure system clock was set

Single-Board Computer and embedded systems might have a clock that is extremely out of sync with reality.
Adding this target ensures docker is only started after a somewhat realistic clock was set.
More information about the time-set.target can be found here: https://www.freedesktop.org/software/systemd/man/systemd.special.html#time-sync.target

Signed-off-by: Michael Kuehn <micha@kuehn.io>

contrib/init/systemd/docker.service

@@ -1,7 +1,7 @@
 [Unit]
 Description=Docker Application Container Engine
 Documentation=https://docs.docker.com
-After=network-online.target docker.socket firewalld.service containerd.service
+After=network-online.target docker.socket firewalld.service containerd.service time-set.target
 Wants=network-online.target containerd.service
 Requires=docker.socket